1. Technical Field
The present invention relates to a light modulator, an optical module, and an image display apparatus.
2. Related Art
As a display apparatus that directly irradiates the retina of a pupil with laser light to allow a user to visually recognize an image, a head mounted display (HMD) and a head-up display (HUD) are known.
Such a display typically includes a light emitting device that emits light and a sweeper that changes the optical path in such a way that the emitted light sweeps the user's retina. The thus configured display allows the user to visually recognize, for example, both an outside scene and an image drawn by the sweeper at the same time.
For example, JP-A-2006-184663 discloses a light beam sweeping display including light sources that emit laser beams of the three primary colors and a deflector that sweeps and projects the laser beams on a screen or any other surface. JP-A-2006-184663 further discloses that the laser beams are deflected in the horizontal and vertical directions for raster sweeping to draw two-dimensional video images.
JP-A-2006-184663 still further discloses that the laser beams are directly modulated by control of the output from each of the light sources on the basis of image data.
In the configuration described in JP-A-2006-184663, in which the laser beams are directly modulated in the light sources, the wavelength of each of the laser beams unintentionally changes in some cases when the ambient temperature and other environmental factors change (wavelength shift). In this case, a shift of the color tone of drawn video images undesirably occurs.
In a case where a diffraction grating is present on the optical path of the light beam sweeping display, the wavelength shift causes a shift of the diffraction angle, resulting in a decrease in the resolution of drawn video images.
To address the problem, a proposal to suppress the wavelength shift by using an external modulator has been made.
An example of the external modulator may include a modulator that includes a substrate in which optical waveguides are formed in parallel to each other and modulates the intensity of light passing through each of the optical waveguides by using an electro-optical effect.
Narrowing the gap between the optical waveguides parallel to each other in the external modulator allows the gap between light fluxes that exit out of the optical waveguides to be narrowed, whereby the resolution of video images to be drawn can be increased.
On the other hand, narrowing the gap between the optical waveguides parallel to each other too much results in crosstalk or optical bond between the optical waveguides, resulting in light loss and color shift.
Further, since the external modulator needs to be provided separately from the light sources, reduction in size of the external modulator is required.